During manufacture of semiconductors and semiconductor microcircuits, it is frequently necessary to coat the materials from which the semiconductors and microcircuits are manufactured with a polymeric organic substance, generally referred to as a photoresist, e.g., a substance which forms an etch resist upon exposure to light. These photoresists are used to protect selected areas of the surface of the substrate, e.g. silicon, SiO.sub.2 or while such etchant selectively attacks the unprotected area of the substrate. Following completion of the etching operation and washing away of the residual etchant, it is necessary that the resist be removed from the protective surface to permit essential finishing operations.
It is necessary in a photolithographic process that the photoresist material, following pattern delineation, be evenly and completely removed from all unexposed areas, in the case of positive resists, or exposed areas in the case of negative resists, so as to permit further lithographic operations. Even the partial remains of a resist in an area to be further patterned is undesirable. Also, undesired resist residues between patterned lines can have deleterious effects on subsequent processes, such as metallization, or cause undesirable surface states and charges.
A common method used in removing the photoresist from the substrate is by contacting the substract with an organic stripper. Heretofore these organic strippers have been composed of various components whose purpose it was to lift and remove the polymeric photoresist from the substrate. However, these stripping solutions have heretofore usually contained phenol or phenol compounds and chlorinated hydrocarbon compounds which resulted in a distinct disadvantage due to the toxicity of phenol as well as the pollution problems arising from the disposal of phenol or phenol compounds such as cresols, phenol sulfonic acid and the like or the disposal of chlorinated hydrocarbon compounds.
Phenol-free and chlorinated hydrocarbons-free strippers are described in U.S. Pat. No. 4,070,203 (issued Jan. 24, 1978 to Neisus et al). These strippers, having only an alkylbenzenesulfonic acid component of 12-20 carbons and a chlorine-free, aromatic hydrocarbon component with a boiling point about 150.degree. C., suffer from the disadvantage that they cannot be easily rinsed off the inorganic substrate after stripping with aqueous rinsing materials such as deionized water. Instead organic solvents are required to avoid either the polymer or the aromatic solvent precipitating or forming oil beads, respectively, or, if water is used, copious amounts are required. The formation of oil beads is called "oiling out" and may lead to an undesirable oily layer remaining on the inorganic substrate.
There are various and numerous drawbacks and disadvantages with the prior art materials. Among the one or more drawbacks and disadvantages found in the use of each such stripping agents there may be mentioned the following: undesirable flammability, volatility, odor and toxicity; incomplete removal of all resist film; effectiveness only on certain resist films; attack of metal substrates by the stripping agent, safety in handling and disposal of the stripper; and the undesired necessity for use at specified elevated temperatures when selected resists are being stripped. Furthermore, the limited stripping capabilities of the stripping agents are a very decided drawback. Additionally, many such strippers are not sufficiently effective against resist materials that are subject to a severe post-baking operation thereby limiting their usefulness. In some of the strippers the presence of water is extremely detrimental. Additionally, for those stripping applications requiring inertness of the agent to metal substrates, toxicity during handling and difficulty of disposal are primary drawbacks.
OSHA, EPA and other similar federal, state and local governmental regulatory agencies have advocated a shift toward use of more human and environmentally compatible stripping compositions and stripping methods that are not subject to the aforementioned drawbacks and problems.
Moreover, heretofore available stripping compositions have required unduly long residence times or repeated applications in order to remove certain coatings. In addition, various coatings have resisted removal from certain substrates with these heretofore available stripping compositions. That is, these previously available stripping compositions have not provided adequate or complete removal of certain hard-to-remove coatings from various substrates.
It is, therefore, highly desirable to provide stripping compositions that exhibit substantially no human or environmental toxicity, and are biodegradable. It is also desirable to provide stripping compositions that are substantially non-corrosive, evidence relatively little, if any, tendency to evaporate and are generally unreactive and also of little toxicity to humans and are environmentally compatible. It would also be most desirable to provide stripping compositions that are recyclable, if desired, and thus available for extended bath life and multiple use.
Moreover, it would be desirable to provide stripping compositions that have a high degree of stripping efficacy and particularly such high degree of stripping efficacy at lower temperatures than generally required with prior stripping compositions.
It is also highly desirable that stripping compositions be provided that exhibit very low vapor pressure at elevated temperatures, thereby significantly reducing evaporation and thus contamination of the atmosphere.
Additionally, it is highly desirable that such compositions be provided that are effective and efficient stripping compositions for removal of coatings from substrates that heretofore have resisted ready removal with conventionally available strippers.
It is also desirable that effective stripping compositions be provided that are devoid of undesirable chlorinated or phenolic components and which do not require the use of hot caustic components. Highly desirable are stripping compositions and use thereof that are not considered undesirable by regulatory agencies overseeing their production and use.
U.S. Pat. No. 4,165,294 to John E. Vander Mey discloses a stripping solution free from phenol and chlorinated hydrocarbons comprising a surfactant, an alkylarylsulfonic acid and an aromatic hydrocarbon having a boiling point above 150.degree. C. The aromatic hydrocarbons are optional and are preferably mixtures of aromatic solvents having 9-13 alkyl carbons and do not comprise more than 40 weight percent.
U.S. Pat. Nos. 4,426,311; 4,395,348; 4,304,681; 4,221,674; 4,215,005 and 4,165,295 each disclose the use of an organic sulfonic acid in a photoresist stripping composition. However, the organic sulfonic acid is utilized in combination with solvents having the aforementioned disadvantages.
It is an object of the invention to provide a non-aqueous biodegradable negative photoresist stripping composition which can be used at a wide range of operating conditions and at lower temperatures.
It is another object of this invention to provide a photoresist stripping solution which is essentially free of phenol, phenol compounds and chlorinated hydrocarbon compounds.
It is an additional object of this invention to provide such a solution which is substantially clean water rinseable such that the hydrocarbon solvent does not oil out and the polymer does not reprecipitate during rinsing.
It is an additional object of this invention to provide a method for removing photoresist polymeric coatings from inorganic substrates with such a stripping solution free from phenol, phenol compounds which can then be rinsed with an aqueous rinsing agent such as deionized water.